The proposed research project is concerned with the morphological and physiological features of the lymphatic capillaries and the role of this system: under normal physiological conditions as well as during the inflammatory response. A detailed ultrastructural investigation of the lymphatic capillaries is being undertaken in an effort to provide information that will further our understanding of the topographic relation of the lymphatic vascular system to the surrounding connective tissue area and the blood vascular system. The removal of interstitial fluids by the lymphatic capillaries is being investigated by following the progress of vital dyes and colloidal substances after interstitial injections. The ontogeny and growth of lymphatics are being studied by using mouse and rat embryos. These ultrastructural and physiological studies on the lymphatic system will provide information that will further our understanding of the development of the system and its involvement in the transfer of interstitial fluids from the connective tissue area into the lymphatic capillaries during both normal and inflamed conditions.